Reproduction: Cloning Around With Mom's Milk

Cloning farm animals from embryos is pretty easy; cattle breeders have been doing it for years. Cloning from full-grown mammals is more difficult, but in the two years since Dolly showed that it was possible, scientists have managed to clone other sheep, mice and even cows, starting with a variety of adult donor tissue. Last week Japanese scientists unveiled what may be the most painless way yet to clone a cow: they produced two healthy Holstein calves from their mother's milk.

The cows were cloned using residual mammary cells found in the yellowish foremilk, or colostrum, produced when a cow gives...